ip.frontiernet.net has no MX records.
Question and response
Question
dig ip.frontiernet.net. MX
Answer
The response has no answer records.
Authority
ip.frontiernet.net. 86400 SOA auth.roch.ny.frontiernet.net. hostmaster.frontier.com. 2508120003 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0